This invention relates to an optical device and a method of manufacturing the optical device.
In order to manufacture an optical device comprising a combination of an optical waveguide of a fiber mount type and optical and electrical components, various methods have been proposed and put into practical use.
For example, Japanese Unexamined Patent Publication (A2) No. H06-347665 (347665/1994) discloses a method of manufacturing an optical device comprising an optical waveguide formed on a substrate on which optical components and electronic devices are mounted. According to this method, a mask pattern for use in sculpturing a V-shaped groove or a groove in the substrate and an electric wiring pattern are formed on the substrate (typically, silicon) by the use of a metal material, such as Au, Al, W, and WSi, which is resistant to an anisotropic etchant and is electrically conductive. On the substrate with the mask and the electric wiring patterns, the optical waveguide is formed by the use of a silica glass material. In order to reduce the production cost, the above-mentioned publication teaches to eliminate a process carried out in presence of step configurations so that high-efficiency optical coupling is achieved between the optical components and the optical waveguide and that mass production on a substrate scale is enabled in all manufacturing steps, including the formation of electrode pads and the electric wiring pattern for the electronic devices. To this end, positioning marks for positioning the optical components such as an optical fiber and an optical semiconductor device, alignment marks for aligning an optical axis of the optical waveguide, the mask pattern, the electric wiring pattern for the optical components and the electronic devices, and the electrode pads are formed on the substrate prior to the formation of the optical waveguide.
As will later be described with reference to the drawings the optical waveguide is partially etched by wet etching or dry etching to define an end plane thereof and to partially expose a substrate surface. Thereafter, the substrate is subjected to anisotropic etching with the mask pattern used as an anisotropic etching mask to form the groove in the substrate. The groove serves to mount the optical fiber.
In the above-mentioned prior art techniques, the mask pattern and the electric wiring pattern are formed before the step configurations are produced by the formation of the optical waveguides. In other words, the mask pattern and the electric wiring pattern are formed on a flat surface of the substrate. This allows mass production of the optical device on a wafer scale by the use of a photolithography process.
However, the above-mentioned prior art technique has following disadvantages.
Specifically, the anisotropic etching mask formed of the above-mentioned metal material may often be altered in characteristic under the influence of the process of forming the optical waveguides over the mask pattern. This is because the heat produced in this process as well as dopant and moisture present in the optical waveguides are inevitably diffused into the mask pattern.
Due to such alteration in characteristic, the anisotropic etching mask loses its resist characteristic against an etchant and no longer serves as a mask. In this situation, the groove of a desired configuration is difficult to obtain.
As a consequence, it is impossible to accurately and reliably mount the optical fiber in the groove.